The present invention relates to a display control circuit and, more particularly, to an effective value voltage stabilizer for a display control circuit in which a power voltage varies over a wide range, and a driving method by the circuit for an electronic apparatus with a solar battery.
FIG. 1 shows a block diagram of the conventional liquid crystal display electronic calculator. SB designates a solar battery, LSI designates a large scale integrated circuit for constructing internal circuits of an electronic calculator, KEY designates a key input device, and LCD designates a liquid crystal display device.
The output voltage of the solar battery SB varies widely in response to incident light. Accordingly, a voltage stabilizer is conventionally provided for stabilizing an applied voltage to compensate for the output voltage of the solar battery SB. The voltage stabilizer comprises a resistance R and a light emitting diode LED. Forward voltage of the light emitting diode LED is used for stabilizing the speed voltage.
FIG. 2 shows a relationship between light and an output voltage A of the solar battery SB or a voltage B supplied to the LSI. L0 designates the minimum light required to drive the display.
In the conventional liquid crystal display apparatus including a solar battery SB, it is necessary that the voltage stabilizer is provided separately from the LSI. The voltage stabilizer is expensive because the LED is included in the voltage stabilizer. Further, packaging space for packaging the voltage stabilizer is additionaly required, so that a compact apparatus may not be assembled.